Blue-Green Algae Blooms
(Our thanks to the Pierce County Environmental Health Department for granting permission to use portions of its Web site for this page.)
Also see state Department of Health brochure on Blue-Green Algae Blooms (PDF)
When you visit local lakes in Thurston County, you might notice a bright green color or thick scum along the shore. This might make you hesitant to take a dip -- and it should! The green color is caused by algae, a primitive plant form that occurs in lakes and streams. Given the right conditions of sunlight, temperature, and nutrients, algae populations can multiply dramatically, often causing a "bloom."
Many lakes in Thurston County are nutrient-rich, or "eutrophic," and experience algae blooms every summer or fall. Algae blooms are a natural occurrence in these nutrient-rich lakes.
Algae come in different shapes, colors and types, some more noticeable than others. Blue-green algae (Cyanophyta), have the nasty possibility of producing toxins (poisons).
What Is A Blue-Green Algae Bloom?
Blue-green algae reproduce rapidly in fresh water when the amount of sunlight, temperature and nutrients are adequate. Within a few days a "clear" lake, pond or ditch can become cloudy with algae growth. This is called a bloom. Blue-green blooms usually float to the surface and can be several inches thick near the shoreline.
A blue-green algae bloom:
Although blue-green blooms can create nuisance conditions and undesirable water quality, most blue-green blooms are not toxic.
What is a Toxic Bloom?
Some blue-green algae produce toxins or poisons. Eventually the toxins break down and are destroyed naturally. Ingesting the algae while they are still poisonous can cause serious illness. In their toxic form, blue-green algae can kill pets, waterfowl, and other animals. Residential drinking water taken from a lake may be affected.
Signs of a toxic bloom may include:
How Can I Tell Whether a Bloom is Toxic?
Whether a particular bloom is actually toxic cannot be determined without special testing. Moreover, testing only provides information on that single sample, at a particular moment of time. Even the scientific experts have not yet solved the mystery of why, when, and how algae turns toxic. In other words, there is no way to predict when, or if, an algae bloom will be toxic. If the water at your beach looks bad, don't swim in it. If you really want to swim, you should find another beach that is clear.
What If I See a Bloom?
When an algae bloom is occurring in a lake, please take these simple precautions:
How You Can Help Prevent Blue-Green Algae Blooms
Algae blooms are likely to occur during sunny, calm weather when high concentrations of nutrients are present in the water. People can have a big effect on the amount of nutrients in a lake. Two important nutrients algae require are phosphorous and nitrogen. These are found in animal and human waste (sewage) and in fertilizers. Excessive amounts of nitrogen and phosphorus may lead to "nutrient loading" and eventually to an algae bloom. To help decrease nutrient loading:
How to Report a Blue-Green Algae Bloom
To report a blue-green algae bloom, call Sue Davis at Thurston County Environmental Health, 867-2500 or e-mail firstname.lastname@example.org.
This page last updated: